In recent years, for wireless communication apparatuses such as cellular phones, there are a plurality of systems that are each in correspondence with a plurality of standards. For example, in Japan, the TDMA system and the CDMA system have gained popularity as cellular phone systems.
Normally, a wireless communication apparatus is configured so as to accommodate any one of the standards. However, given the restrictions imposed on frequency bands allocated to the respective systems due to the proliferation of terminals, recent cellular phone systems reflect a transition to multiband. In addition, in order to provide stable and sophisticated service, a transition to multiband is also performed involving handoffs between different frequency bands and communication carried out among a plurality of communication systems (for example, 1x and 1xEVDO).
As such a multiband-capable wireless communication apparatus, for example, a cellular phone terminal is known which combines the TDMA system with the CDMA system and couples a TDMA transmitting/receiving unit and a CDMA transmitting unit to a primary antenna and a CDMA receiving unit to a secondary antenna (for example, refer to Japanese Patent Laid-Open No. 2004-15162).
In addition, more recently, a multiband-capable cellular phone terminal is being considered which is equipped with a SHDR (Simultaneous Hybrid Dual Receiver) function in which transmission/reception of a system is performed by a primary antenna while reception of another system is performed by a secondary antenna in order to improve communication throughput by the primary antenna.
FIG. 8 is a functional block diagram showing a schematic configuration of substantial parts of a cellular phone terminal equipped with such a SHDR function.
The cellular phone terminal is provided with: a 1x communication system which uses a 800 MHz band-cdma 2000 system (hereinafter abbreviated as 800 MHz band when appropriate) and a 2 GHz band-cdma 2000 system (hereinafter abbreviated as 2 GHz band when appropriate); a 1xEVDO (hereinafter simply abbreviated as EVDO when appropriate) communication system; and an 1575.42 MHz (hereinafter abbreviated as 1.5 GHz band when appropriate) GAS frequency receiving capability, and includes a transmitting unit (Tx) 101 connected to a baseband unit 100 having a modulating circuit and a demodulating circuit, a primary receiving unit (primary Rx) 102, and a secondary receiving unit (secondary Rx) 103.
The transmitting unit 101 and the primary receiving unit 102 are connected to a primary antenna 105 via a duplexer 104, and are capable of transmission/reception at the 800 MHz band and the 2 GHz band. In addition, the secondary receiving unit 103 is connected to a secondary antenna 106 and is independently capable of reception at the 800 MHz band, the 2 GHz band and the 1.5 GHz band.
The cellular phone terminal adopts a diversity system for EVDO communication and is arranged to regularly receive, during such EVDO communication, informative information (paging) notifying 1x communication from a base station to monitor incoming call, and is provided with a hybrid mode and an SHDR mode that uses the SHDR function as operating modes.
In the hybrid mode, as shown in FIG. 9(a), during EVDO communication, the primary antenna 105 side is regularly switched to 1x communication to receive paging. Moreover, in the hybrid mode, there are cases where the secondary antenna 106 side is synchronized with the primary antenna 105 side to perform diversity reception of 1x communication paging. Meanwhile, in the SHDR mode, as shown in FIG. 9(b), incoming call is monitored by having the primary antenna 105 side continue EVDO communication and regularly switching the secondary antenna 106 side to 1x communication to receive paging.
In this case, in the SHDR mode, as shown in FIG. 9(b), since EVDO communication is continued on the primary antenna 105 side without switching to 1x communication, EVDO communication throughput can be improved compared to the hybrid mode.
However, since the secondary antenna 106 receives three bands, namely, the 800 MHz band, the 2 GHz band, and the 1.5 GHz band, antenna gains at the 800 MHz band and the 2 GHz band are generally lower compared to the primary antenna 105 which performs transmission/reception in two bands, namely, the 800 MHz band and the 2 GHz band. For example, as shown in FIG. 10(a), while the antenna gains of the primary antenna 105 at the 800 MHz band and the 2 GHz band are, respectively, −3 dBi and 0 dBi, the antenna gains of the secondary antenna at the 800 MHz band and the 2 GHz band 106 are, respectively, −10 dBi and −3 dBi. Therefore, the SHDR mode has a lower capturing capability of paging from a base station as compared to the hybrid mode.
In this light, conventionally, as shown in FIG. 8, an actual 1x reception sensitivity received at the primary receiving unit 102 or the secondary receiving unit 103 and inputted to the baseband unit 100 is compared at a mode switching unit 108 to an upper bound threshold and a lower bound threshold of 1x reception sensitivity stored beforehand in a threshold memory 107. Based on the comparison result, as shown in FIG. 11, the baseband unit 100, the transmitting unit 101, the primary receiving unit (primary Rx) 102 and the secondary receiving unit (secondary Rx) 103 are controlled so as to switch to the SHDR mode when the 1x reception sensitivity exceeds the upper bound threshold during the hybrid mode and switch to the hybrid mode when the 1x reception sensitivity falls to or below the lower bound threshold during the SHDR mode.
In other words, when switching modes, as described in the flowchart shown in FIG. 12, the hybrid mode is first set as a default operating mode (step S111), a judgment is made on whether a 1x paging is to be received or not or, in other words, a judgment is made on whether a 1x search is to be executed or not (step S112), and when a 1x search is to be executed, next, an operating mode of the mode switching unit 108 at that point is judged (step S113).
At this point, when the operating mode is judged to be the hybrid mode, as shown in FIG. 9(a), EVDO communication and 1x reception are performed on the primary antenna 105 side while EVDO communication diversity reception is performed on the secondary antenna 106 side (step S114). In this case, since a 1x paging is received by the primary antenna 105 having a high antenna gain, next, a judgment is made by the mode switching unit 108 on whether an actual 1x reception sensitivity supplied from the baseband unit 100 exceeds an upper bound threshold or not (step S115), and if not, the routine transitions to step S112. In addition, if the 1x reception sensitivity exceeds the upper bound threshold, since a 1x paging is receivable by the secondary antenna 106 whose antenna gain is low, the operating mode is switched from the hybrid mode to the SHDR mode with a high throughput (step S116), and the routine transitions to step S112.
Meanwhile, in step S113, when the operating mode is judged to be the SHDR mode, as shown in FIG. 9(b), EVDO communication is performed on the primary antenna 105 side while EVDO communication diversity reception and 1x reception are performed on the secondary antenna 106 side (step S117). In this case, since a 1x paging is received by the secondary antenna 106 having a low antenna gain, next, a judgment is made by the mode switching unit 108 on whether an actual 1x reception sensitivity supplied from the baseband unit 100 is equal to or lower than a lower bound threshold or not (step S118), and if not, the routine transitions to step S112. In addition, if the 1x reception sensitivity is equal to or lower than the lower bound threshold, since the capturing capability of 1x paging must be increased, the operating mode is switched from the SHDR mode to the hybrid mode (step S119), and the routine transitions to step S112 while arranging 1x paging to be received by the primary antenna 105 having a high antenna gain.